1. Field of the Invention
The present invention relates to an apparatus and a method for partitioning moving picture data and, in particular, to an apparatus and a method for partitioning DCT coefficient information in order to perform error tolerance transmission of moving picture information.
2. Description of the Background Art
According to popularization of digital image services such as a digital TV broadcast including a high definition TV, a digital versatile disc (DVD) is attracting public attention as a new multimedia device. MPEG (moving picture experts group) is the international standard for defining streaming video and audio over a communication network. It is regulated by the ISO/IEC (international electrotechnical commission) of the ISO (international standard organization). Standardization of MPEG has proceeded with the cooperation of the international telecommunication union (ITU).
The MPEG standard partly concerns coding video and audio information stored in a digital storage medium. However, at present its application is expanded to multimedia database access or radio multimedia communication. In particular, MPEG-2 has been developed as a multimedia standard for next generation broadcast, such as a HDTV and a digital satellite broadcast. Presently MPEG-4 is a multimedia coding method, and it is a kind of system protocol for defining interface with a communication network.
FIG. 1 is a block diagram illustrating a construction of an encoder used for a data partitioning method in accordance with the conventional art. As depicted in FIG. 1, the encoder includes a first combining unit 1 for adding a received video signal to a compensated signal; a DCT unit 2 for performing DCT (discrete cosine transform) of a signal outputted from the first combining unit 1; a quantizing unit 3 for quantizing a signal of the DCT unit 2; an inverse-quantizing unit 4 for inverse-quantizing a signal outputted from the quantizing unit 3; and an IDCT (inverse discrete cosine transform) unit 5 for performing IDCT of a signal outputted from the inverses-quantizing unit 4.
Also included are a second combining unit 6 for combining an output signal of the IDCT unit 5 with an output signal of a motion compensating unit 9; a frame memory 7 for clipping and storing a signal outputted from the second combining unit 6; a motion judging unit 8 for estimating motion through a signal of the frame memory 7 and a received video signal; a motion compensating unit 9 for compensating motion by reflecting the estimation judged in the motion judging unit 8 in the signal stored in the frame memory 7; and a data partitioning unit 10 for receiving a result judged in the motion judging unit 8 and the signal of the quantizing unit 3 and outputting data-partitioned streams.
The data partitioning method is a technique for partitioning a video stream into not less than two parts. The data partitioning method used for encoding standardization is for separating motion information and metro block header from a DCT coefficient. In video stream transmission, if part of texture information consisting of the DCT coefficient is lost, the texture information is disregarded, and accordingly reproduction screen is constructed only with motion information. However, in an encoding frame in a screen, because there is no motion information, the DCT coefficient loss has a bad effect upon a picture quality of a moving picture.
In order to reduce an error due to the DCT coefficient loss, a spectrum separation method for separating the DCT coefficient into two parts has been presented. In the DCT coefficient, visually important low frequency components are allocated to a priority part, and the rest of high frequency components are allocated to a background (lower priority) part.
FIG. 2 shows a bit string structure of the data partitioning method used for the MPEG-2 standard, and arrows (A, B, C, D) indicate decoding orders. In the MPEG-2 standard, the DCT coefficient is divided into a partition 0 corresponding to a priority part and a partition 1 corresponding to a background (lower priority) part, construction part included in the partition 0 is determined by a priority breakpoint. In more detail, by the priority breakpoint value, it is determined whether how many coefficients are included in the priority part (partition 0), and the rest low frequency parts are included in the background part.
The spectrum separation method can provide error immunity about the DCT coefficient, however, picture quality of the priority part is considerably lowered in comparison with a single stream having the same bit rate. Accordingly, when error occurs in the background part, although screen is constructed only with the priority part, there is not such a big gain.
FIGS. 3A and 3B show a bit string structure of the data partitioning method used for the MPEG-4 standard. Herein, FIG. 3A shows frames between screens, and FIG. 3B shows frames in a screen. In frames between screens, a macro block header and motion information are separated from the DCT coefficient and are allocated to the priority part, and the DCT coefficients is allocated to the background part. In frames in a screen, only a DC coefficient is allocated to the priority part with a macro block header, and the rest AC coefficient is allocated to the background part.
In general, when an error occurs in the background part, an encoder has to reconstruct a screen by using the priority part information. In more detail, if the DCT coefficient of the frames between the screens is lost due to a transmission error, the encoder reconstructs the damaged macro block with motion information. If the background part of the frame in the screen is lost due to an error, the encoder has to reconstruct the macro block only with the DC coefficient. In addition, if an error occurs-in the priority part, the encoder has to disregard the encoded all information.
In the current method for partitioning moving picture data, the spectrum separation method does not include all frequencies in the priority part. Therefore, picture quality in the priority part is remarkably lowered in comparison with a single stream having the same bit rate. In more detail, due to error occurred in the background part, a picture quality-lowering problem occurs seriously in reproducing of the screen only with the priority part. A system and method is needed that can overcome the above shortcoming.